The present invention relates to an improved system and method for bone preparation for an implant. In particular, the present invention relates to a computer assisted surgical system and method for resecting bone to receive an orthopedic implant for press-fit applications.
Arthroplasty or joint replacement surgical procedures require accurate bone preparation for the implantation of prosthetic components i.e., implants. A precise fit between the implant and resected bone is desired for good fixation in both cementless and cemented applications in order to prevent loosening of the implant over time. Furthermore, an interference fit or “press-fit” is often desired to ensure good fixation of the implant to the bone, and for osteointegration of cementless devices. The amount of interference fit to apply, however, is difficult to ascertain and often determined by empirical methods with the benefit of intra-operative evaluations of the patient's bone.
For example, in a total knee joint replacement surgery, the distal femur, proximal tibia and patellar articulating surfaces are replaced with prosthetic components. The femoral component typically requires that the distal femur be resected with e.g., five bone cuts that are made at angles to one another when viewed from a sagittal perspective. The bone cuts are commonly performed with a bone cutting tool, such as a saw or a mill that is guided by a manual cutting block or a template.
Surgical cutting blocks can have integrated cutting slots or open surfaces that correspond to the inner shape of the implant to be used. These guiding surfaces are at fixed distances and angles from one another so that one cutting block must be provided for each size and shape of the implant or a limited range of sizes of the type of implant.
Implants used in cementless applications often incorporate a porous coating about its bone interface surface. The porous coating is typically structured so as to be dimensionally offset from the implant's bone interface surface. That is, the porous coating typically sits proud of the implant's bone interface surface. However, regardless of whether or not an implant is to be used for cemented or cementless applications, the bone preparation i.e., bone cuts are typically the same. That is, the same cutting blocks/jigs are used to guide the bone cuts for implants used for either cementless or cemented applications. Therefore, the resulting discrepancy between the bone cut formed using the cutting block and the internal bone interface surface of the implant (which may be at least in part determined by the thickness of the coating) provides a nominal degree of press-fit interference between the bone cuts as established by the cutting block and the implant once it is impacted onto the resected bone. Alternatively, a manual cutting block can be used with cutting planes that are slightly offset and/or angled from the inner surfaces of the implant to achieve a predetermined and fixed amount of interference.
One of the challenges orthopaedic surgeons face in the operating room is the varying quality of bone they are presented with at surgery. Patients undergoing joint replacement surgery typically suffer from degenerative conditions that can alter bone quality. Thus, from one patient to another, the surgeon may encounter varying degrees of bone quality. For example, upon exposing the patient's joint and bones, the surgeon may encounter bone that is very poor in quality, having a relatively low density or high porosity. On other occasions, for example, in younger more active patients, the bone can be relatively dense and hard. The quality of bone can affect the degree or tightness of the fit of the implant for a given amount of interference. Hence, when bone cuts are prepared in the same fashion for all patients, the resulting tightness or degree of the fit can vary from one patient to another depending upon the bone quality, which may ultimately impact the overall short term and long term success of the implant. However, there are currently no tools available that allows the surgeon to precisely and objectively adjust the bone cuts during a surgical procedure in order to customize the degree of press-fit interference between the implant and resected bone for individual patients that takes into account the varying quality of bone of individual patients.
Another disadvantage of conventional systems used in arthroplasty is that they lack flexibility in the ability to adjust the relative positions of the bone cuts for any particular implant, which can allow for varying the resulting degree of interference press-fit achieved between the resected bone and the implant being used. Additionally, conventional systems cannot provide multiple levels of interference press-fit in an all-in-one device. For example, in a manual set of instruments, once the cutting blocks are manufactured they cannot be changed and the surgeon needs to accept those relative cut locations for all patients and surgical circumstances.
Therefore, a need still exists for a system and method for the preparation of bone to receive an implant that can provide intra-operative flexibility to a surgeon user and allow for variations in the degree of press-fit interference provided based upon pre or intra-operative assessment of the patient e.g., bone quality and implant trialing. Such a need is met by the system and method of the present invention.